Retirement Plans - Narrative (Details) - Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits - USD ($)	3 Months Ended	9 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024	Dec. 31, 2024
Defined Contribution Plan Disclosure [Line Items]
DCP participant deferrals	$ 0	$ 43,000	$ 0	$ 144,000
Contributions by employer	0	0	0	0
Deferred compensation plan expense	$ 6,033,000	$ 6,983,000	$ 12,371,000	$ 13,665,000
Class B Common Stock
Defined Contribution Plan Disclosure [Line Items]
Shares reserved for issuance (in shares)	50,000,000		50,000,000
Shares reserved for future issuance (in shares)	4,616,129		4,616,129
Phantom shares issuable (in shares)	10,827,233		10,827,233		12,728,808

Deferred Compensation Arrangement With Individual, Compensation Expense (Income)

No definition available.

Name:	bsy_DeferredCompensationArrangementWithIndividualCompensationExpenseIncome
Namespace Prefix:	bsy_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Dividends, Common Stock, Stock, Issuable

+ References

No definition available.

+ Details

Name:	bsy_DividendsCommonStockStockIssuable
Namespace Prefix:	bsy_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Aggregate number of common shares reserved for future issuance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Topic 210
-SubTopic 10
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(29))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1

+ Details

Name:	us-gaap_CommonStockCapitalSharesReservedForFutureIssuance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of common shares reserved for future issuance related to deferred compensation arrangements with individuals.

+ References

No definition available.

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualCommonStockReservedForFutureIssuance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Amount of contributions made by employer into fund established for purposes of making future disbursement to individual in accordance with deferred compensation arrangement.

+ References

No definition available.

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualContributionsByEmployer
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of distribution made to individual in accordance with deferred compensation arrangement.

+ References

No definition available.

+ Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualDistributionPaid
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 70
-Name Accounting Standards Codification
-Section 50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480794/715-70-50-1

+ Details

Name:	us-gaap_DefinedContributionPlanDisclosureLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DeferredCompensationArrangementWithIndividualPostretirementBenefitsByTypeOfDeferredCompensationAxis=us-gaap_DeferredCompensationArrangementWithIndividualByTypeOfCompensationPensionAndOtherPostretirementBenefitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementClassOfStockAxis=us-gaap_CommonClassBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: